In an access network, multicast (MC) technology has been widely used to deliver multicast service flows (e.g., a multicast service in an interactive network Television (IPTV)) from an operator side to subscriber networks. Upstream MC (i.e. multicast data from the subscriber subnet) is not allowed. The access device just discards the multicast data from the subscriber networks. However, the multicast in the subscriber networks is sure to exist. For example, a user in the subscriber networks intends to multicast his/her existing video or live performance to his/her friends and relatives; or the headquarters multicast a CEO's speech to his branches. On the other hand, network operators would like to provide more value-added services to attract more subscribers to thereby earn more profits, thus the network operators earnestly need a solution that can effectively support Upstream MC (UP-MC) services.
Currently, there exist several UP-MC solutions, one being that the subscriber terminal unicasts the service data to be sent to multiple receivers, respectively; and the other being that the subscriber terminal unicasts the service data to be sent to a server in the network, and then it is the server that forwards the multicast packets of the service data.
Currently, in the access network, the Spanning Tree Protocol (STP, see IEEE 802.d standard for details) or Rapid Spanning Tree Protocol (RSTP, see IEEE 802.w standard for details) are widely supported, wherein a device at the network side and remote from the subscriber network is taken as a root node, thereby generating a spanning tree, then the multicast packets from the network side are sent on the spanning tree. As to the access network shown in FIG. 1, the Broadband Remote Access Server (BRAS) connected at the network side is the root of the spanning tree. For a UP-MC from the subscriber terminal UE1, the solution is as follows: a access device A1 transmits the multicast packets along the existing spanning tree to S1, and then S1 transmits it along the spanning tree path to the subscriber terminals UE2 and UE3 that receive the multicast packets. Or, the subscriber terminal UE1 transmits the multicast packets to the access device A1 thereof, then the access device A1 tunnels the multicast packets to the network device (for example BNG, Broad Network Gateway) close to the root node of the spanning tree, and then the BNG forwards the packets on the existing spanning tree.
In the above solutions, the UP-MC and other services (unicast service, IPTV service) share a common logic topology which is derived by calculating the STP or the RSTP. For the UP-MC services, the path from the UP-MC sending end to the corresponding receiving end is not a better one. For example, as far as the UP-MC receiving subscriber terminal UE2 under the access device A2 is concerned, the best path from the UP-MC sending subscriber terminal UE1 under the access device A1 to the MP-US receiving subscriber terminal UE2 is A1-S4-S5-A2, rather than A1-S2-S1-S3-S4-S5-A2, or A1-S2-S1-BNG-S1-S3-S4-S5-A2.
The above UP-MC solutions waste much network bandwidth with a greater transmission delay.